This invention relates to the optical positioning and alignment of an optical fiber and an optical component such as a collimating lens.
During assembly, optical systems having multiple optical elements must be precisely optically aligned. Absent such optical alignment, there may be significant transmission losses within the optical system. The misalignment transmission losses between each pair of optical elements is multiplied with increasing numbers of optical elements, so that misalignments in complex systems may result in a large attenuation of the optical energy in the light beam. The input light beam may not be arbitrarily increased in power to account for these transmission losses, as some of the optical elements are typically limited as to the power levels that they can transmit without damage to the optical elements.
In one important example, when a light beam leaves an optical fiber there is some angular dispersion in the light beam. The light beam is thereafter collimated by a collimating lens before passing to other optical elements. The optical fiber axis at the output end of the optical fiber must be precisely positioned and aligned with the collimating lens and the downstream optical elements to avoid transmission losses at this point of the optical system.
The positioning of the optical components to accomplish their precision alignment has traditionally been accomplished using a mechanical alignment process. In the case of aligning an optical fiber to other optical components, the outer surface of the outer jacket of the optical fiber is grasped, usually in a bushing-like hollow tube, and mechanically aligned manually. The present inventors have recognized that this approach has significant shortcomings, both because the light-transmitting core of the optical fiber may not be locally coaxial with the outer surface of the outer jacket, and because there is significant likelihood that operator fatigue and inattention will adversely affect the alignment procedure. There is a substantial possibility that the attempted alignment will not be precise, and that the error in the alignment will not be predictable or repeated.
There is a need for an improved approach to the positioning and optical alignment of optical systems that achieves improved optical alignment and also avoids operator error. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method for optically positioning an optical fiber and an optical component along an optical axis, leading to an accurate alignment of the optical fiber and the optical component. The method is highly precise and repeatable, and does not rely on any assumption as to the coaxiality of the core and the outer jacket of the optical fiber. It may be automated so that it is not dependent upon the performance of the human operator.
In accordance with the invention, a method for optically positioning an optical fiber and an optical component along an optical axis comprises the steps of furnishing the optical fiber having an alignment end with an optical fiber axis, and furnishing the optical component, which may be of any type but is preferably a collimating lens such as a gradient-index-of-refraction lens. The alignment end of the optical fiber may be its input end or its output end, but is preferably its output end. The alignment end of the optical fiber is positioned so that the optical fiber axis is coincident with the optical axis, and light (preferably visible light) passing through the optical fiber is focused upon an imaging light detector. The optical component is not present on the optical axis during the positioning of the optical fiber, but it is thereafter inserted onto the optical axis. The method further includes coarse positioning the optical component using light (preferably visible light) transmitted through the optical fiber and through the optical component to be incident upon a light energy detector, and thereafter fine positioning the optical component using light (preferably infrared light) transmitted through the optical fiber and through the optical component to be incident upon the imaging light detector.
The alignment end of the optical fiber and the optical component are preferably each mounted in their own alignment stages to accomplish the positioning steps. The alignment end of the optical fiber is preferably mounted in a five-degree-of-freedom optical-fiber alignment stage that allows the alignment end to be moved parallel to the optical axis, translated in two mutually perpendicular directions in a plane perpendicular to the optical axis, and angularly adjusted in two mutually perpendicular angles each lying in planes that include the optical axis. The optical component is preferably mounted in a six-degree-of-freedom optical-component alignment stage that permits the optical component to be moved parallel to the optical axis, translated in two mutually perpendicular directions in a plane perpendicular to the optical axis, angularly adjusted in two mutually perpendicular angles each lying in planes that include the optical axis, and rotated about the optical axis. Rotation of the optical component about the optical axis during both the coarse positioning and the fine positioning aids in achieving a precise alignment of the optical component.
The optical-fiber alignment stage and the optical-component alignment stage are each preferably automated so that the various movements are accomplished by motors in the alignment stages. The motors are driven by a feedback controller functioning responsive to the respective outputs of the imaging light detector and the light energy detector.
After the positioning and alignment, the aligned positions of the alignment end of the optical fiber and the optical component are fixed responsive to the steps of positioning the output end of the optical fiber and fine positioning the optical component.
The method described above may be practiced with any operable apparatus. Preferably, it utilizes a light source system having a light-source light output and including a visible-light source, an infrared-light source, and a light mixer that mixes the visible-light output and the infrared-light output to produce the light-source light output. The optical fiber is mounted so that the light-source light output is directed through the optical fiber. There is a light-detector system to receive the light-source light output from the optical fiber. The light-detector system has an imaging light detector having an imaging-light-detector output signal, and a light energy detector having a light-energy-detector output signal.